I'm... not exactly sure, but I THINK Google has taken another step to prevent us from downloading content off of YouTube - lately, I've tried downloading certain videos as MP3s for specific songs, only to find that they won't work. For instance, KeepVid has a extension site for downloading videos as MP3s, however it doesn't work anymore; likewise, I know there's a few YouTube-to-MP3 conversion sites out there and I've used them before with no problem, but now they don't work, and I believe one of them actually did come up with an error message that the video/song was copyrighted and couldn't be downloaded.
This seems to only effect videos that are matched third party by whoever holds the rights to the song (ala ones that have that little ad next to the video description, telling you to buy the song on iTunes).
This seems to only effect videos that are matched third party by whoever holds the rights to the song (ala ones that have that little ad next to the video description, telling you to buy the song on iTunes).